Regenerative braking, coupled with the recent technology advance in hybrid electric vehicles (HEVs) and electric vehicles (EVs), provides a promising route to reduce fuel consumption and emission. With regenerative braking, the kinetic energy of a vehicle can be converted back into electric energy, which is stored in an energy storage system, typically a battery, for future use.
As implemented in HEVs and EVs, regenerative braking in many parts of the world is regulated by the following regulations: European Directive 71/320/EEC; UNECE (United Nations Economic Commission for Europe) Regulation 13H for Cars (M1) and optionally Light Commercials (N1); and UNECE Regulation 13.11 for virtually all other vehicles. The corresponding document for U S manufactured vehicles is known as “Federal Motor Vehicle Safety Standard 135—Light Vehicle Brake Systems (U.S. Department of Transportation, 2005).” A vehicle manufacturer is required to comply with one or more of these regulations.
The above regulations, e.g., Regulations 13H and 13.11, define two categories, namely, Category A and Category B, of regenerative braking systems (RBS). Specifically, “Category A” RBS is not part of a vehicle's service brake system (i.e., friction brakes) and is only controlled by a driver through the accelerator/throttle and/or the gear neutral position. In contrast, “Category B” RBS is part of the service brake system. Category B RBS may be activated at the same time or slightly after the service brake system is activated (i.e., “parallel” or “non-phased” braking strategy), or be controlled to deliver regenerative braking torque ahead of the development of the friction braking torque (i.e., “serial” or “phased” braking strategy).
Category A RBS operates independently from the service brake system. That is, the input of Category A RBS does not depend on input on the brake pedal and the output (i.e., regenerative braking torque) of Category A RBS does not need to be blended with the friction braking torque. Thus, compared to Category B RBS, Category A RBS requires simpler hardware design and software control scheme, and costs less. Moreover, because Category A RBS does not need to be integrated into the service brake system, which is usually a separate module sold by brake suppliers, Category A RBS can be developed and/or customized by the vehicle manufacturers and customers.
Despite the above advantages, the maximum energy recoverable by a conventional Category A RBS is limited by the movable range of the accelerator/throttle. After the accelerator/throttle is fully released, the RBS is unable to produce any additional braking torque. The disclosed regenerative braking control method and system are directed to mitigating or overcoming one or more of the problems set forth above and/or other problems in the prior art.